1. Field of the Invention
Embodiments disclosed herein generally relate to a cutting element. Specifically, embodiments disclosed herein relate to a non-uniform interface for a cutting element.
2. Background Art
In a typical drilling operation, a drill bit is rotated while being advanced into a soil or rock formation. The formation is cut by cutting elements on the drill bit, and the cuttings are flushed from the borehole by the circulation of drilling fluid that is pumped down through the drill string and flows back toward the top of the borehole in the annulus between the drill string and the borehole wall. The drilling fluid is delivered to the drill bit through a passage in the drill stem and is ejected outwardly through nozzles in the cutting face of the drill bit. The ejected drilling fluid is directed outwardly through the nozzles at high speed to aid in cutting, flush the cuttings, and cool the invention.
The present invention is described in terms of cutter elements for roller cone drill bits, although its benefits can be realized in percussion bits as well as other fixed cutter bits. Referring to FIG. 1A, in a typical roller cone drill bit 150, the bit body 151 supports three roller cones 153 that are rotatably mounted on cantilevered journals (not shown), as is well known in the art. Each roller cone in turn supports a plurality of cutting elements 159, which cut and/or crush the wall or floor of the borehole and thus advance the bit.
Referring now to FIG. 1B, conventional cutting inserts 166 typically have a body 168 consisting of a cylindrical grip portion from which a convex cutting end 170 extends. In order to improve their operational life, these inserts are sometimes coated with a superhard, sometimes also known as an ultrahard, material. The coated cutting layer typically comprises a superhard substance, such as a layer of polycrystalline diamond (PCD). The substrate, which supports the cutting layer is normally formed of a hard material such as tungsten carbide (WC). The grip is embedded in and affixed to the roller cone and the cutting end extends outwardly from the surface of the roller cone. The protrusion, for example, may be hemispherical, which is commonly referred to as a semi-round top (SRT), or may be conical, or chisel-shaped, or may form a crest that is inclined relative to the plane of intersection between the grip and the cutting end.
Although cutting elements having various shapes have significantly expanded the scope of formations for which drilling with diamond bits is economically viable, the interface 172 between the substrate and the diamond layer continues to limit usage of these cutter elements, as it is prone to failure. Specifically, it is not uncommon for diamond coated inserts to fail during cutting. Failure typically takes one of three common forms, namely spalling/chipping, delamination, and wear. External loads due to contact tend to cause failures such as fracture, spalling, and chipping of the diamond layer. The impact mechanism involves the sudden propagation of a surface crack or internal flaw initiated on the PCD layer, into the material below the PCD layer until the crack length is sufficient for spalling, chipping, or catastrophic failure of the enhanced insert. On the other hand, internal stresses, for example, thermal residual stresses resulting from manufacturing processes, tend to cause delamination of the diamond layer, either by cracks initiating along the interface and propagating outward, or by cracks initiating in the diamond layer surface and propagating catastrophically along the interface. Excessively high contact stress and high temperature, along with a very hostile downhole operation environment, are known to cause severe wear to the diamond layer of cutting elements in roller cone drill bits. The wear mechanism occurs due to the sliding of the PCD relative to the earth formation.
It has been found that chipping, spalling, and delamination are common failure modes for cutting elements having ultrahard surfaces. Accordingly, there exists a need for a more durable cutting element which may reduce the occurrence of spalling and/or delamination.